This invention relates to a method and apparatus for locating an abnormality in a gas-insulated electric device, operative to determine the spot of an insulation abnormality, which occurs inside a metallic container, from outside of the metallic container.
When a gas-insulated electric device having a high-voltage conductor supported by being insulated within a metallic container filled with insulation gas has developed an insulation abnormality and is left intact, it can result in such a serious accident as insulation breakdown. Therefore, it is necessary to locate, from outside of the metallic container, the abnormality at the stage of its symptom such as the emergence of a partial discharge, thereby taking appropriate counter measures. For this purpose, there have been proposed various methods and apparatus for locating abnormalities in gas-insulated electric devices.
An example of proposals, as disclosed in Japanese Patent Unexamined Publication No. 62-245976, employs a plurality of detectors disposed inside the metallic container and operates to locate an abnormality on the basis of the difference in propagation time of abnormality signals detected by the detectors. The electric device abnormality detection system of this example comprises detection units each made up of a reactor, which is disposed in each of contiguous metallic containers interleaved by insulation segments and adapted to detect a voltage generated by a partial discharge, and a measuring unit connected across the reactor, and a location confinement unit which confines the spot of partial discharge on the basis of the timing relationship of the detected signals provided by the detection units. Voltages created across the reactors of detection units due to a partial discharge are detected by the associated measuring units, and they produce detected signals of different timings for the spot confinement unit, which then confines the spot of abnormality based on the time differences of the detected signals.
Another example proposed in Japanese Patent Unexamined Publication No. 59-136661 is designed to locate an abnormality by detecting a discharge light emission which emerges at the occurrence of a partial discharge. The detection system of this example comprises a plurality of optical conductors disposed by the interior surface of a cylindrical sealed container, in which a gas-insulated conductor is accommodated, along the longitudinal direction of the container, and each having a light receptive end surface at a position different among the light conductors, a transparent protective member fitted on the sealed container to cover the exterior section of the light conductors, a receiving electrode made of a porous plate material which covers the exterior section of the protective member, and a signal lead-out device which leads the signal from the electrode and the signals from the light conductors out of the sealed container. This arrangement is capable of detecting a partial discharge at a virtually constant sensitivity irrespective of its location along the axis of the gas-insulated electric device, and locating the spot of discharge.
A further example, which is proposed in the proceeding of the 19th Electrical Insulation Material Symposium held from Sep. 30 until Oct. 1, 1986, entitled "Insulation diagnosis for a conduit air electric transmission line using AE sensors", is designed to detect the sound of collision of a foreign object thereby to locate the spot of incident.
However, the conventional methods and apparatus for locating an abnormality in a gas-insulated electric device, as described above, do not impart the spot of abnormality with a satisfactory accuracy. Depending on the location of a partial discharge and its severity, prompt inspection of the spot of abnormality is required in some cases, and the inspection and recovery activities for the abnormality must be done as quick and less influence on the power supply operation as possible. On this account, the accurate location of the spot of abnormality is needed, which however cannot be accomplished by use of the conventional methods and apparatus for locating abnormalities. Moreover, it is not possible for the conventional methods and apparatus to locate a very small partial discharge, which is still harmful depending on the cause of incident and its location, and therefore a more sensitive method and apparatus for locating the spot of abnormality have been desired.